Lithographic printing is a form of printing which uses specially prepared printing surfaces that have regions which are capable of accepting ink (i.e., oleophilic) surrounded by background areas which are oleophobic in that they do not accept ink. Today there are two commercial methods of preparing the printing surfaces referred to as dry and wet processes, respectively. In both processes the printing surfaces are formed on plates.
Certain lithographic printing plates are used in a dry process called dryographic printing. These plates have highly ink repellent areas formed by a silicon layer and other areas which are highly absorbent of ink. A second, more commonly used process employs a wet printing plate where both water and/or an aqueous dampening liquid as well as a greasy ink are applied to the plate surface that contains the hydrophilic and hydrophobic areas. Those areas which are water attractive will soak the water or the dampening liquid and thereby be rendered oleophobic. In contrast, the hydrophobic areas repel the water but accept the ink.
There are several examples of known prior art processes by which a photo-responsive material can be made image-wise receptive or repellent to ink upon exposure. These include the processes set forth in U.S. Pat. No. 5,401,611 and U.S. Pat. No. 4,034,183. In general, these optical or photographic processes employ a substance which will either be rendered oleophilic or oleophobic upon exposure to light. The '611 method employs steps of an image-wise exposure to actinic radiation by a heat mode recording material. The material has a support having a hydrophilic surface or is provided with a hydrophilic layer and a metallic layer. On top of these layers is a hydrophobic layer having a thickness of less than 50 nanometers, thereby rendering the exposed areas hydrophilic and repellent to greasy ink. The '611 recording material is characterized by a hydrophobizing agent that has a specific chemical formula.
The '183 recording material is also heat sensitive and has a hydrophilic layer that sits on an anodized aluminum support. The '183 heat mode recording material is selectively exposed using a laser and the exposed areas are thereby rendered hydrophobic, and thus ink is accepted by the material.